A radial turbine has a configuration in which a plurality of centrifugal blades are fixed to a hub secured to a rotating shaft, and in which working fluid, i.e., air or gas, flowing from the radially outer circumferential side toward the inner side through a flow path between a nozzle mount and a nozzle plate, which have a ring-like shape and are provided substantially parallel to each other, acts on the centrifugal blades to rotate the hub and is discharged substantially in an axial direction.
In the flow path between the circular plates, a plurality of nozzle vanes for accelerating the working fluid are arranged with gaps therebetween in the circumferential direction.
A variable geometry radial turbine has a configuration in which the nozzle vanes are supported by shafts on the nozzle mount and turn on the shafts to open or close throat spaces formed by adjacent nozzle vanes, thereby enabling adjustment of the flow rate, flow velocity, etc., of the fluid discharged.
In the variable geometry radial turbine, because the nozzle vanes turn in this way, end surfaces of the nozzle vanes move along the nozzle mount and the nozzle plate accordingly. Therefore, in order to prevent the drawback that the end surfaces of the nozzle vanes touch the nozzle mount and the nozzle plate, thus becoming immobilized, gaps must be provided between the end surfaces of the nozzle vanes and the nozzle mount and between the end surfaces of the nozzle vanes and the nozzle plate.
These gaps serve as fluid leakage paths and, thus, decrease the efficiency of the variable geometry radial turbine. The influence of this decrease is significant particularly when the flow rate is low, i.e., when the nozzle vanes are closed.
For example, PTL (Patent Literature) 1 proposes a turbine that suppresses fluid leakage when the nozzle vanes are closed, thereby suppressing a decrease in efficiency occurring when the flow rate is low.
The turbine suppresses fluid leakage from the gaps by providing plate-like projections on leading edges of nozzle vanes and on trailing edges of nozzle vanes adjacent thereto when the nozzle vanes are at a closed position.